REQUIRED METHOD OF RESYNCHRONIZING LTU'S MODEMS

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP88-00893R000200080030-2
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 2
• Document Creation Date: December 12, 2016
• Document Release Date: May 17, 2002
• Sequence Number: 30
• Publication Date: October 5, 1978
• Content Type: REQ

PROJECT COORDINATION NOT'" PCN # : D-2
Approved For Release 2002/06/19 : CIA-RDP88-00893R44D200080030-2
Project : MAXCON Date : 5 October 1978
Author : Sponsor Project Team Member r- f F , 9 2.3
Approval : Sponsor COTR
A
Required Method of Resynchroniz
Subject
ing LTU's Modems
Distribution Sponsor Project Team
STATINTL
This PCN documents the necessary handshaking to properly
resynchronize the modems attached to the LTUs once resynchronization
has been determined to be necessary. The information comes from the
Collins Radio Company publication of the instruction manual for the
87846-1 Modem Termination Unit (MTU). It Is applicable to the Mixer,
DLA, and MTU handlers to be used with PIAXCON.
When the processor determines that a resynchronization is
-necessary, "...it immediately generates a sync command which Is routed
to the MTU as a supervisory command word...The MTU, when it recognizes
the sync command, responds by generating a 20 tplus or minus 103
-3nillisecond sync command signal which is routed to the modem
=transmission facility..."
This sync command signal is referred to by the Sponsor as SI
or Sync Initiate. The signal from the LTU to he used as the SI signal
-iS the Terminal Ready signal.
"...When the modem transmission facility receives the sync
,command [the Terminal Ready line pulsing for approx. 20 milliseconds]
from the MTU, the modem transmission facility responds by forcing the
sync-in-progress line...to a logic one (1) level. This action notifies
the MTU that the modem transmission facility is in the process of
-resynchronizing the modem transmission link. The MTU responds to the
sync-in-progress command by inhibiting both the transmit and the
receive data. If the processor queries the MTU during this period, the
MTU responds by generating a sync-in-progress supervisory monitor
word ...When the modem transmission link is finally synchronized, the
sync-in-progress line returns to a logic zero (0). With this action,
the MTU begins to generate a minimum of 24 sync idle characters which
are then routed to the modem transmission facility on the transmit
data line...When at least 24 sync idle characters have be generated by
the transmit control circuit and three (3) sync idle characters have
been counted by the receive control circuit..., the MTU is prepared
for normal operation. When the processor now queries the MTU, the PITU
will respond by generating an in-sync/operate supervisory word ..."
The above description shows the -interaction between the MTU
,and the modem transmission facility. The Sponsor refers to his
Approved For Release 2002/06/19 : CIA-RDP88-00893R000200080030-2
 PROJECT COORDINATION NOTr PCN # D-2
Approved For Re g se 2002/06/19: CIA-RDP88-00893R0.Qg200080030-2
.sync-in-progress line as the SIP or the Sync-In-Progress line, so
little adaptation is necessary. The signal line to the LTU to he used
for this line is the Clear-to-Send line. Since the modem transmission
facility (modem) may resynchronize due to factors beyond the LTU's
control, the LTU shall have to await the resynchronization of the
modem as if it initiated the resynchronization to begin with. Issuance
and reception of sync idle characters shall have to follow this
non-LTU initiated resynchronization as well.
Approved For Release 2002/06/19 : CIA-RDP88-00893R000200080030-2